Method of building a tunnel and tunnel built according to said method

ABSTRACT

In order to prevent sinking of a tunnel the invention provides a less expensive method of building a tunnel in the bottom of a body of water, whereby a tunnel trench is dredged in said bottom and a foundation layer, supporting said tunnel elements, is arranged in said tunnel trench, in that the tunnel trench is dredged till a depth of at least twice the tunnel height under the bottom surface of said tunnel to be built, in which trench a ballast bed of foundation material, like sand, is arranged.

United States Patent De Koning et al.

[ METHOD OF BUILDING A TUNNEL AND TUNNEL BUILT ACCORDING TO SAID METHOD Inventors: Jan De Koning, Amsterdam; Romke Assignee:

Filed:

Appl. No.:

Van Der Veen, Jutphaas, both of Netherlands Ballast-Nedam Group N.V., Amsterdam, Netherlands Apr. 16, 1973 US. Cl 61/433; 61/724 Int. Cl E02d 29/06 Field of Search 61/43, 44, 72.4, 72.3, 61/721 References Cited UNITED STATES PATENTS Dunham 61/43 1451 June 24, 1975 1,647,448 11/1927 Jones 61/43 2,107,671 2/1938 Killmer 61/84 2,164,003 6/1939 Scheelhaase 61/46 3,568,455 3/1971 McLaughlin et a1 61/72.1 3,656,309 4/1972 Bultema 61/43 X 3,665,718 5/1972 Griffioen et al. 61/43 Primary Examiner-Dennis L. Taylor Attorney, Agent, or Firm-John P. Snyder [57] ABSTRACT In order to prevent sinking of a tunnel the invention provides a less expensive method of building a tunnel in the bottom of a body of water, whereby a tunnel trench is dredged in said bottom and a foundation layer, supporting said tunnel elements, is arranged in said tunnel trench, in that the tunnel trench is dredged till a depth of at least twice the tunnel height under the bottom surface of said tunnel to be built, in which trench a ballast bed of foundation material, like sand, is arranged.

5 Claims, 3 Drawing Figures '1 METHOD OF BUILDING A TUNNEL AND TUNNEL BUILT ACCORDING SAID METHOD The invention relates toa method of buildinga tunnel in thebottom bf'a' body of water, comprising a'senel elements to sink said mud hasto be removed from the trench, e.g. by means of a' mud dredger in order to prevent settlement of the tun n el asare'sult of the presence of mud enclosures below the tunnel.

As a result of cutting the various ground layers during dredging the tunnel trench the bottom'inclines to settle. in order-to prevent settlement of the bottom with a tunnel built therein, with the known method the tunnel is positioned in a track especially sochosen, that it does not contain ground layers contributing to settlement,

I but incorporating the disadvantage that a longer tunnel has to be built to achieve a bank connection and that often longer roads meeting the tunnel have to be constructed at the banks. At the known method a material improving the soil, e.g. bentonite or cement, is injected into the ground or piles are driven into the ground in,

order to prevent settlement of the tunnel. All these measures avoiding settlement of the tunnel are expensive. With the known method the tunnel trench is dredged to an accurately determined level e.g. with a bucket dredger, which is expensive especially when the tunnel is lying at a large depth, e.g. 30 m, under the water surface.

The invention provides a less expensive method preventing sinking of the tunnel, in that said tunnel trench is dredged till a depth of at least twice the tunnel height. under the bottom surface of said tunnel to be built, in which trench a ballast bed of foundation material, like sand, is arranged.

The method according to the invention of dredging the tunnel trench at a large depth requires removal of much soil. As these dredging activities require less accuracy, said activities can take place even up to e.g. 80 m with a deep sucking dredger with a very high capacity and as a result not very expensive. As the ballast bed carrying the weight of the tunnel, is able to support at large depth at the ground lying underneath, said ground can be of low quality because of the high static pressure prevailing in said ground. As the tunnel trench is dredged deeply, all the mud moving in the vicinity over the water bottom accumulates in said tunnel trench, said mud being able to be sucked up easily and to be removed to a remote spot, so that just before, during and after the sinking of the tunnel elements no inconvenience is caused by mud. If necessary some time is waited with arranging the ballast bed into the tunnel,

trench, so that all the neighbouring mud has extra time for getting into the tunnel trench.

The invention relates to and provides further a tunnel, constructed according to the method of the invention, of a series of interconnected tunnel elements and,

characterized by a ballast bed of foundation material, like sand, arranged in the bottom and having a thickness of at least twice the tunnel height.

' According to HO. 1 in a bottom 2 lying under water The invention will be elucidated. in the following description with reference to a drawing:

In the drawing: v

FIGS: 1 and 2 show one and the same cross section through a tunnel trench in two stages during performing the method: according to the invention; and,

FlGf3a longitudinal section over line Illlll of FIG.

1 a tunnel trench 13 is" dredged by means" of a suction dredger 20, said bottom 2' mainly consisting of sand 8,

with gravel enclosures 3, bog layers 4 and clay layers :5, said dredger 20 comprising a vessel l 5, 'a' pump 17 arranged on a frame l 6 swingably suspended on the vessel 15, said pump 17being positioned undera body .of', water 1, a suction pipe 18 being connected to the pump 17' and a delivery pipe 19 being connected to the pump 17, said delivery pipe 19 extending far outside the drawn working area of the tunnel trench 13 in which material, e.g. mud 7, moving to and fro and over the bottom 2 by tide stream, is collected. When the lower surface 21 of the tunnel elements 10 at a depth B of e.g. 40 in has to be positioned under the water 1, a tunnel trench 13 of e.g. a depth C of m is dredged underwater, so that under the lower surface 21 an additional depth D is dredged, at least amounting twice the tunnel height a of e.g..8 m, preferably however, amounting more as shown in this example. The tunnel slot 13 is dredged so steeply and so deeply, that the mud 7, found in the tunnel trench, cannot rise along the walls 24. The collected mud 7, as well as the soil from the tunnel trench is sucked up by means of a suction dredger 20 and conveyed outside the tide transport stream belonging to the tunnel trench 13.

The layers 3, 4 and 5 are cut through during dredging the tunnel trench 13. Settlement of the tunnel 6 is prevented by partly filling the tunnel trench 13 with a heavy ballast bed 9 of foundation material, like sand with a thickness d of about 30 m. Thanks to the great mass of the ballast bed settlings in the layers 3, 4 and 5 outside the tunnel trench 13 do not cause settlement of the tunnel 6. The tunnel elements 10 are positioned by means of provisional support means 22, e.g. jacks at a height e of e.g. 20 cm, over the ballast bed 9 consisting of sand and filled up with additional sand 23, after which the tunnel 6 is covered with a sand layer 11 of e.g. 10 m.

FIG. 3 shows the tunnel from bank 14 to bank 14 to show that the support layer, formed by the ballast bed 9 offers a safe support of the tunnel 6, while the bottom 2 lying under water itself is not suitable for supporting a tunnel 6, received therein.

What we claim is:

l. The method of building a tunnel in the bottom of a body of water, which tunnel comprises a series of interconnected tunnel elements, comprising the steps of dredging a tunnel trench in said bottom till a depth which is several times the tunnel height is reached, partially filling said trench with a ballast bed of foundation material to a depth below said bottom but at least twice the height of said tunnel laying the tunnel in the partially filled trench in temporarily supported position above the level of the foundation material, and then completing the filling of said trench with foundation material substantially to the level of said bottom whereby to encompass and bury said tunnel.

2. The method of building a tunnel as defined in claim 1 including the step, prior to partial filling of the trench, of collecting migrating material such as mud on the bottom for a time sufficient to assure minimal further migration of such material and removing such ma terial by suction dredging.

3. The method of building a tunnel as defined in claim 2 wherein completing the filling is effected in two stages the first of which comprises filling foundation material directly beneath the tunnel.

4. The method of building a tunnel beneath a body of water, comprising the steps of:

a. operating a suction dredger to form a trench in the bottom below the body of water and in which the trench is of a depth at least several times the height a of the tunnel to be built;

b. filling said trench with foundation material such as sand to a level below said bottom but at least twice v said height of the tunnel;

c. sinking tunnel sections and joining them end-toend while temporarily supported above the level of said foundation material; and then d. completing the filling of said trench with foundation material substantially to the level of said bottom whereby to encompass and bury said tunnel sections.

5. The method as defined in claim 4 wherein material dredged in step (a) is discharged sufficiently remote from said trench as substantially to preclude migration of such dredged material back into said trench, and including the step prior to step (b) of collecting and suction dredging from said trench migrating material such as mud on the bottom surface which migrates naturally into said trench for a time sufficient to assure minimal further migration during steps (b), (c) and (d). 

1. The method of building a tunnel in the bottom of a body of water, which tunnel comprises a series of interconnected tunnel elements, comprising the steps of dredging a tunnel trench in said bottom till a depth which is several times the tunnel height is reached, partially filling said trench with a ballast bed of foundation material to a depth below said bottom but at least twice the height of said tunnel laying the tunnel in the partially filled trench in temporarily supported position above the level of the foundation material, and then completing the filling of said trench with foundation material substantially to the level of said bottom whereby to encompass and bury said tunnel.
 2. The method of building a tunnel as defined in claim 1 including the step, prior to partial filling of the trench, of collecting migrating material such as mud on the bottom for a time sufficient to assure minimal further migration of such material and removing such material by suction dredging.
 3. The method of building a tunnel as defined in claim 2 wherein completing the filling is effected in two stages the first of which comprises filling foundation material directly beneath the tunnel.
 4. The method of building a tunnel beneath a body of water, comprising the steps of: a. operating a suction dredger to form a trench in the bottom below the body of water and in which the trench is of a depth at least several times the height of the tunnel to be built; b. filling said trench with foundation material such as sand to a level below said bottom but at least twice said height of the tunnel; c. sinking tunnel sections and joining them end-to-end while temporarily supported above the level of said foundation material; and then d. completing the filling of said trench with foundation material substantially to the level of said bottom whereby to encompass and bury said tunnel sections.
 5. The method as defined in claim 4 wherein material dredged in step (a) is discharged sufficiently remote from said trench as substantially to preclude migration of such dredged material back into said trench, and including the step prior to step (b) of collecting and suction dredging from said trench migrating material such as mud on the bottom surface which migrates naturally into said trench for a time sufficient to assure minimal further migration during steps (b), (c) and (d). 